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make clang emit undefs for padding of structs and unions instead of zeros. this enables constant compaction optimizations.

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llvm-svn: 85504
This commit is contained in:
Nuno Lopes
2009-10-29 11:27:06 +00:00
parent 901668f306
commit 09bd8656c3
3 changed files with 5 additions and 5 deletions
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6
clang/lib/CodeGen/CGExprConstant.cpp
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@@ -228,7 +228,7 @@ class VISIBILITY_HIDDEN ConstStructBuilder {
if (NumBytes > 1)
Ty = llvm::ArrayType::get(Ty, NumBytes);
llvm::Constant *C = llvm::Constant::getNullValue(Ty);
llvm::Constant *C = llvm::UndefValue::get(Ty);
Elements.push_back(C);
assert(getAlignment(C) == 1 && "Padding must have 1 byte alignment!");
@@ -266,7 +266,7 @@ class VISIBILITY_HIDDEN ConstStructBuilder {
if (NumBytes > 1)
Ty = llvm::ArrayType::get(Ty, NumBytes);
llvm::Constant *Padding = llvm::Constant::getNullValue(Ty);
llvm::Constant *Padding = llvm::UndefValue::get(Ty);
PackedElements.push_back(Padding);
ElementOffsetInBytes += getSizeInBytes(Padding);
}
@@ -496,7 +496,7 @@ public:
if (NumPadBytes > 1)
Ty = llvm::ArrayType::get(Ty, NumPadBytes);
Elts.push_back(llvm::Constant::getNullValue(Ty));
Elts.push_back(llvm::UndefValue::get(Ty));
Types.push_back(Ty);
}

2
clang/test/CodeGen/cast-to-union.c
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@@ -1,5 +1,5 @@
// RUN: clang-cc -emit-llvm %s -o - | FileCheck %s
// CHECK: w = global %0 { i32 2, [4 x i8] zeroinitializer }
// CHECK: w = global %0 { i32 2, [4 x i8] undef }
// CHECK: y = global %union.u { double 7.300000e+0{{[0]*}}1 }
// CHECK: store i32 351, i32

2
clang/test/CodeGen/union-init2.c
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@@ -1,4 +1,4 @@
// RUN: clang-cc -emit-llvm %s -o - -triple i686-pc-linux-gnu | grep "bitcast (%0\* @r to %union.x\*), \[4 x i8\] zeroinitializer"
// RUN: clang-cc -emit-llvm %s -o - -triple i686-pc-linux-gnu | grep "bitcast (%0\* @r to %union.x\*), \[4 x i8\] undef"
// Make sure we generate something sane instead of a ptrtoint
union x {long long b;union x* a;} r = {.a = &r};